Question about 1.8T AEB motor and MAF limits for Big Turbo upgrade

[Moes]

HI so long time stalker, first time poster in this area.

I'm looking at buying a 98-99 VW Passat or Audi A4 with the 1.8T AEB motor and I've read a lot about how you can run K04 or Big Turbo on the stock ECU with a tune and add larger injectors/Adjustable Fuel pressure Regulator (along with FMIC/Exhaust ect). But I see a lot of people seem to run into the 5.0V MAF limmit according to their Vag-com. Basically their Turbo is flowing more air than the MAF can read. I see people run larger injectors and increase or decrease fuel pressure to account for the additional air but it seems like a tuning "gray area" once you max out the MAF. I see some people drill holes aft of the MAF to let more air in but this is "un-metered air" per the ECU and Tune.

I've read that you can try VR6 MAF's from a VW Jetta Mk 3 or 4 but would this MAF work with a Passat ECU in a "plug and play" fashion? I assume not. I see 034 motor sports makes a billet Alu MAF also but I'm not sure how they are different.

So my main questions boils down to, assume I'm running a AEB motor with a K04 get close to 15-20PSI (or where ever the MAF maxes out) what are my options if I want to run a Big Turbo on a built motor down the road? can I still incorporate the stock ECU with a tune and some kind of modified MAF? I know other people are running BT on AEB's and can't seem to find a straight answer on how they do it other than "custom tuning"..

I'm seriously contemplating buying a B5.5 PAssat or B6 A4 with a AWM motor just so I don't run into this problem down the road when I can do a Big Turbo build since that motor has a MAP and I assume helps in adding another tuning options to meter air?

[walky_talky20]

Whilst the 2001+ ECU's (Bosch Motronic ME7) are the better tuning platform, it is not so much because they have a MAP sensor. In fact, it's not really a MAP (Manifold Absolute Pressure) sensor. It is just a boost sensor, because the sensor is not located in the manifold and never sees vacuum. You can't "run off just the MAP sensor". That sensor has literally no data at idle.

The real reason they are better is because of the Wideband oxygen sensor. The entire programming of the ECU is different as it is always able to see the Air/Fuel Ratio (AFR), and it will attempt to hit and maintain the "target AFR" at all times. Even wide open throttle. This is how all the later EFI engines run, so the tuners are focusing their expertise there. A lot of tuners don't even mess with the older narrowband and cable throttle cars. Indeed many of them weren't out of gradeschool when those cars were new. So you have more options with the DBW/wideband setup.

That said, the MAF problem isn't fixed by going with an AWM car. It's still there. The fix, however, is the same. You enlarge the MAF housing (Inner Diameter) from 2.5" (stock) to 2.75" (TT 225/VR6) or 3" (S4) or 3.25" (Audi 4.2 V8). Don't take those numbers as gospel, but basically speaking - there are drop-in OEM upgrades for MAF size.

Key thing, though: when you upsize the housing, the MAF sensor reads lower. Kinda the point to keep from maxing it out. But you have to adjust the ECU software to interpret the lower numbers and still deliver the right amount of fuel. So MAF size and injector size are pretty much specified by your tune.

Hope that helps.

[thrilos5]

You will need to scale your MAF to work with the big turbo and injectors through ecu software